CVE-2026-97971 (GCVE-0-2026-97971)

Vulnerability from cvelistv5 – Published: 2026-09-25 10:23 – Updated: 2026-09-25 14:41
VLAI
Title
nstree: check listing permission before taking a namespace reference
Summary
In the Linux kernel, the following vulnerability has been resolved: nstree: check listing permission before taking a namespace reference legitimize_ns() takes a reference on the candidate namespace before may_list_ns() has decided whether the caller may see it. The __free(ns_put) cleanup on the denied path can drop the last reference to a mount namespace while we still hold the rcu read lock, and put_mnt_ns() may sleep there. This is the same problem commit 2ec2aff3c8e2 ("ns: make sure reference are dropped outside of rcu lock") fixed for the put_user() path. Neither ns_requested() nor may_list_ns() needs a reference, both only look at the namespace type and at the caller's own namespaces, so do the checks first and take the reference last. Splat: Voluntary context switch within RCU read-side critical section! WARNING: kernel/rcu/tree_plugin.h:332 at rcu_note_context_switch+0x238/0x2a0, CPU#5: a/3442 CPU: 5 UID: 1000 PID: 3442 Comm: a Not tainted 7.0.0-30-generic #30-Ubuntu PREEMPT(lazy) RIP: 0010:rcu_note_context_switch+0x238/0x2a0 Call Trace: <TASK> __schedule+0xcf/0x650 schedule+0x27/0x90 schedule_preempt_disabled+0x15/0x30 __mutex_lock.constprop.0+0x550/0xaf0 __mutex_lock_slowpath+0x13/0x20 mutex_lock+0x3b/0x50 exp_funnel_lock+0xb2/0x260 synchronize_rcu_expedited+0xe7/0x220 namespace_unlock+0x26a/0x320 put_mnt_ns+0xd3/0x120 mntns_put+0xe/0x20 do_listns+0x13e/0x560 __do_sys_listns+0x126/0x2d0 __x64_sys_listns+0x20/0x30 x64_sys_call+0x2366/0x2390 do_syscall_64+0x105/0x5a0 entry_SYSCALL_64_after_hwframe+0x76/0x7e </TASK>
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 76b6f5dfb3fda76fce1f9990d6fa58adc711122b , < 9e673bf5d88aa898e52cef5c87058c3fa845bc71 (git)
Affected: 76b6f5dfb3fda76fce1f9990d6fa58adc711122b , < 56ea4e86832d8abe8930394473566c194d189f85 (git)
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Linux Linux Affected: 6.19
Unaffected: 0 , < 6.19 (semver)
Unaffected: 7.2.7 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc3 , ≤ * (original_commit_for_fix)
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      "affected": [
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          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnstree: check listing permission before taking a namespace reference\n\nlegitimize_ns() takes a reference on the candidate namespace before\nmay_list_ns() has decided whether the caller may see it. The\n__free(ns_put) cleanup on the denied path can drop the last reference to a\nmount namespace while we still hold the rcu read lock, and put_mnt_ns()\nmay sleep there. This is the same problem commit 2ec2aff3c8e2 (\"ns: make\nsure reference are dropped outside of rcu lock\") fixed for the put_user()\npath. Neither ns_requested() nor may_list_ns() needs a reference, both\nonly look at the namespace type and at the caller\u0027s own namespaces, so do\nthe checks first and take the reference last.\n\nSplat:\n\n  Voluntary context switch within RCU read-side critical section!\n  WARNING: kernel/rcu/tree_plugin.h:332 at rcu_note_context_switch+0x238/0x2a0, CPU#5: a/3442\n  CPU: 5 UID: 1000 PID: 3442 Comm: a Not tainted 7.0.0-30-generic #30-Ubuntu PREEMPT(lazy)\n  RIP: 0010:rcu_note_context_switch+0x238/0x2a0\n  Call Trace:\n   \u003cTASK\u003e\n   __schedule+0xcf/0x650\n   schedule+0x27/0x90\n   schedule_preempt_disabled+0x15/0x30\n   __mutex_lock.constprop.0+0x550/0xaf0\n   __mutex_lock_slowpath+0x13/0x20\n   mutex_lock+0x3b/0x50\n   exp_funnel_lock+0xb2/0x260\n   synchronize_rcu_expedited+0xe7/0x220\n   namespace_unlock+0x26a/0x320\n   put_mnt_ns+0xd3/0x120\n   mntns_put+0xe/0x20\n   do_listns+0x13e/0x560\n   __do_sys_listns+0x126/0x2d0\n   __x64_sys_listns+0x20/0x30\n   x64_sys_call+0x2366/0x2390\n   do_syscall_64+0x105/0x5a0\n   entry_SYSCALL_64_after_hwframe+0x76/0x7e\n   \u003c/TASK\u003e"
        }
      ],
      "metrics": [
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            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
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              "lang": "en",
              "value": "AV:L - The bug is reached only through the local listns() syscall (SYSCALL_DEFINE4(listns) -\u003e do_listns()/do_listns_userns() -\u003e legitimize_ns()). No remote protocol supplies any input.\nAC:L - The attacker controls both sides of the race. One process loops listns() while another creates and tears down its own mount namespaces with unshare(CLONE_NEWUSER|CLONE_NEWNS), so legitimize_ns() ends up holding the last reference on the may_list_ns() denied path.\nPR:L - listns() has no capability gate, and may_list_ns() only filters what is returned after the reference is taken. The commit\u0027s splat shows the trigger from UID 1000, and the victim mount namespaces can be created without privilege through user namespaces.\nUI:N - The attacker\u0027s own syscalls produce both the listing and the namespace teardown. No other user takes part.\nS:U - This is corruption and a hang inside the kernel\u0027s own namespace and RCU handling. No hypervisor, IOMMU or other separately governed boundary is crossed.\nC:H - put_mnt_ns() queues call_rcu(mnt_ns_release_rcu) and then sleeps in synchronize_rcu_expedited() inside do_listns()\u0027s rcu_read_lock. On non-preemptible-RCU kernels that lets the mnt_namespace be kfree\u0027d, and next_ns_common(ns) then walks list pointers read from freed memory.\nI:H - After the use-after-free, the iterator hands a freed, reallocatable object to legitimize_ns(), which increments its refcount through ns_get_unless_inactive() and calls ns-\u003eops-\u003eput(). That gives a write primitive and an indirect call through attacker-sprayable memory.\nA:H - On PREEMPT_RCU kernels, synchronize_rcu_expedited() called from within the caller\u0027s own RCU read-side section waits on itself and hangs the task. Elsewhere the result is a sleeping-in-atomic BUG or a use-after-free crash, and an unprivileged user can repeat it at will."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-25T14:41:46.399Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/9e673bf5d88aa898e52cef5c87058c3fa845bc71"
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        {
          "url": "https://git.kernel.org/stable/c/56ea4e86832d8abe8930394473566c194d189f85"
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      "title": "nstree: check listing permission before taking a namespace reference",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-97971",
    "datePublished": "2026-09-25T10:23:11.539Z",
    "dateReserved": "2026-09-25T10:18:58.207Z",
    "dateUpdated": "2026-09-25T14:41:46.399Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
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        "descriptions": [
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            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnstree: check listing permission before taking a namespace reference\n\nlegitimize_ns() takes a reference on the candidate namespace before\nmay_list_ns() has decided whether the caller may see it. The\n__free(ns_put) cleanup on the denied path can drop the last reference to a\nmount namespace while we still hold the rcu read lock, and put_mnt_ns()\nmay sleep there. This is the same problem commit 2ec2aff3c8e2 (\"ns: make\nsure reference are dropped outside of rcu lock\") fixed for the put_user()\npath. Neither ns_requested() nor may_list_ns() needs a reference, both\nonly look at the namespace type and at the caller\u0027s own namespaces, so do\nthe checks first and take the reference last.\n\nSplat:\n\n  Voluntary context switch within RCU read-side critical section!\n  WARNING: kernel/rcu/tree_plugin.h:332 at rcu_note_context_switch+0x238/0x2a0, CPU#5: a/3442\n  CPU: 5 UID: 1000 PID: 3442 Comm: a Not tainted 7.0.0-30-generic #30-Ubuntu PREEMPT(lazy)\n  RIP: 0010:rcu_note_context_switch+0x238/0x2a0\n  Call Trace:\n   \u003cTASK\u003e\n   __schedule+0xcf/0x650\n   schedule+0x27/0x90\n   schedule_preempt_disabled+0x15/0x30\n   __mutex_lock.constprop.0+0x550/0xaf0\n   __mutex_lock_slowpath+0x13/0x20\n   mutex_lock+0x3b/0x50\n   exp_funnel_lock+0xb2/0x260\n   synchronize_rcu_expedited+0xe7/0x220\n   namespace_unlock+0x26a/0x320\n   put_mnt_ns+0xd3/0x120\n   mntns_put+0xe/0x20\n   do_listns+0x13e/0x560\n   __do_sys_listns+0x126/0x2d0\n   __x64_sys_listns+0x20/0x30\n   x64_sys_call+0x2366/0x2390\n   do_syscall_64+0x105/0x5a0\n   entry_SYSCALL_64_after_hwframe+0x76/0x7e\n   \u003c/TASK\u003e"
          }
        ],
        "id": "CVE-2026-97971",
        "lastModified": "2026-09-25T15:18:03.220",
        "metrics": {
          "cvssMetricV31": [
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                "attackComplexity": "LOW",
                "attackVector": "LOCAL",
                "availabilityImpact": "HIGH",
                "baseScore": 7.8,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "LOW",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
                "version": "3.1"
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              "impactScore": 5.9,
              "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
              "type": "Secondary"
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        "published": "2026-09-25T11:17:24.980",
        "references": [
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            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Received"
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    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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